#include "config.hpp"
#include <atomic>
#include <cassert>
#include <csignal>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <fcntl.h>
#include <inttypes.h>
#include <iostream>
#include <netdb.h>
#include <netinet/tcp.h>
#include <sys/epoll.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/un.h>
#include <thread>
#include <unistd.h>
#include <vector>

std::atomic<bool> shutdown_requested{false};

#ifndef __has_feature
#define __has_feature(x) 0
#endif

void signal_handler(int sig) {
  if (sig == SIGTERM || sig == SIGINT) {
    shutdown_requested.store(true, std::memory_order_relaxed);
  }
}

// Adapted from getaddrinfo man page
int getListenFd(const char *node, const char *service) {

  struct addrinfo hints;
  struct addrinfo *result, *rp;
  int sfd, s;

  memset(&hints, 0, sizeof(hints));
  hints.ai_family = AF_UNSPEC;     /* Allow IPv4 or IPv6 */
  hints.ai_socktype = SOCK_STREAM; /* stream socket */
  hints.ai_flags = AI_PASSIVE;     /* For wildcard IP address */
  hints.ai_protocol = 0;           /* Any protocol */
  hints.ai_canonname = nullptr;
  hints.ai_addr = nullptr;
  hints.ai_next = nullptr;

  s = getaddrinfo(node, service, &hints, &result);
  if (s != 0) {
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
    abort();
  }

  /* getaddrinfo() returns a list of address structures.
     Try each address until we successfully bind(2).
     If socket(2) (or bind(2)) fails, we (close the socket
     and) try the next address. */

  for (rp = result; rp != nullptr; rp = rp->ai_next) {
    sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
    if (sfd == -1) {
      continue;
    }

    int val = 1;
    setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));

    // Set socket to non-blocking for graceful shutdown
    int flags = fcntl(sfd, F_GETFL, 0);
    if (flags != -1) {
      fcntl(sfd, F_SETFL, flags | O_NONBLOCK);
    }

    if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0) {
      break; /* Success */
    }

    close(sfd);
  }

  freeaddrinfo(result); /* No longer needed */

  if (rp == nullptr) { /* No address succeeded */
    fprintf(stderr, "Could not bind\n");
    abort();
  }

  int rv = listen(sfd, SOMAXCONN);
  if (rv) {
    perror("listen");
    abort();
  }

  return sfd;
}

int getAcceptFd(int listenFd, struct sockaddr_storage *addr) {
  // Use sockaddr_storage (not sockaddr) to handle both IPv4 and IPv6
  socklen_t addrlen = sizeof(sockaddr_storage);
  int fd = accept4(listenFd, (struct sockaddr *)addr, &addrlen, SOCK_NONBLOCK);
  return fd;
}

// Connection lifecycle. Only one of these is the case at a time
//  - Created on an accept thread from a call to accept
//  - Waiting on connection fd to be readable/writable
//  - Owned by a network thread, which drains readable and writable bytes
//  - Owned by a thread in the request processing pipeline
//  - Closed by a network thread according to http protocol
//
// Since only one thread owns a connection at a time, no synchronization is
// necessary
// Connection ownership model:
// - Created by accept thread, transferred to epoll via raw pointer
// - Network threads claim ownership by wrapping raw pointer in unique_ptr
// - Network threads transfer back to epoll by releasing unique_ptr to raw
// pointer
// - RAII cleanup happens if network thread doesn't transfer back
struct Connection {
  const int fd;
  const int64_t id;
  struct sockaddr_storage addr; // sockaddr_storage handles IPv4/IPv6

  Connection(struct sockaddr_storage addr, int fd, int64_t id)
      : fd(fd), id(id), addr(addr) {}

  ~Connection() {
    int e = close(fd);
    if (e == -1) {
      perror("close");
      abort();
    }
  }

  struct Task {
    std::string s;
    bool closeConnection{false};
    int written = 0;
  };

  std::deque<Task> tasks;

  void readBytes(size_t max_request_size) {
    // Use smaller buffer size but respect max request size
    // TODO revisit
    size_t buf_size = std::min(size_t(4096), max_request_size);
    std::vector<char> buf(buf_size);
    for (;;) {
      int r = read(fd, buf.data(), buf.size());
      if (r == -1) {
        if (errno == EINTR) {
          continue;
        }
        if (errno == EAGAIN) {
          return;
        }
        perror("read");
        goto close_connection;
      }
      if (r == 0) {
        goto close_connection;
      }
      // "pump parser"
      // TODO revisit
      tasks.emplace_back(std::string{buf.data(), size_t(r)});
    }
  close_connection:
    tasks.emplace_back(std::string{}, true);
  }

  bool writeBytes() {
    while (!tasks.empty()) {
      auto &front = tasks.front();
      if (front.closeConnection) {
        return true;
      }
      int w;
      for (;;) {
        w = write(fd, front.s.data() + front.written,
                  front.s.size() - front.written);
        if (w == -1) {
          if (errno == EINTR) {
            continue; // Standard practice: retry on signal interruption
          }
          if (errno == EAGAIN) {
            return false;
          }
          perror("write");
          return true;
        }
        break;
      }
      assert(w != 0);
      front.written += w;
      if (front.written == int(front.s.size())) {
        tasks.pop_front();
      }
    }
    return false;
  }

#if __has_feature(thread_sanitizer)
  void tsan_acquire() { tsan_sync.load(std::memory_order_acquire); }
  void tsan_release() { tsan_sync.store(0, std::memory_order_release); }
  std::atomic<int> tsan_sync;
#else
  void tsan_acquire() {}
  void tsan_release() {}
#endif
};

int main(int argc, char *argv[]) {
  std::string config_file = "config.toml";

  if (argc > 1) {
    config_file = argv[1];
  }

  auto config = weaseldb::ConfigParser::load_from_file(config_file);

  if (!config) {
    std::cerr << "Failed to load config from: " << config_file << std::endl;
    std::cerr << "Using default configuration..." << std::endl;
    config = weaseldb::Config{};
  }

  std::cout << "Configuration loaded successfully:" << std::endl;
  std::cout << "Server bind address: " << config->server.bind_address
            << std::endl;
  std::cout << "Server port: " << config->server.port << std::endl;
  std::cout << "Max request size: " << config->server.max_request_size_bytes
            << " bytes" << std::endl;
  std::cout << "Accept threads: " << config->server.accept_threads << std::endl;
  std::cout << "Network threads: " << config->server.network_threads
            << " (0 = auto)" << std::endl;
  std::cout << "Event batch size: " << config->server.event_batch_size
            << std::endl;
  std::cout << "Min request ID length: " << config->commit.min_request_id_length
            << std::endl;
  std::cout << "Request ID retention: "
            << config->commit.request_id_retention_hours.count() << " hours"
            << std::endl;
  std::cout << "Subscription buffer size: "
            << config->subscription.max_buffer_size_bytes << " bytes"
            << std::endl;
  std::cout << "Keepalive interval: "
            << config->subscription.keepalive_interval.count() << " seconds"
            << std::endl;

  signal(SIGPIPE, SIG_IGN);
  signal(SIGTERM, signal_handler);
  signal(SIGINT, signal_handler);

  int sockfd = getListenFd(config->server.bind_address.c_str(),
                           std::to_string(config->server.port).c_str());
  std::vector<std::thread> threads;
  int epollfd = epoll_create(/*ignored*/ 1);
  if (epollfd == -1) {
    perror("epoll_create");
    abort();
  }

  // Network threads - use config value, fallback to hardware concurrency
  int networkThreads = config->server.network_threads;
  if (networkThreads == 0) {
    // TODO revisit
    networkThreads = std::thread::hardware_concurrency();
    if (networkThreads == 0)
      networkThreads = 1; // ultimate fallback
  }

  // Event batch size from configuration
  for (int i = 0; i < networkThreads; ++i) {
    threads.emplace_back(
        [epollfd, i, max_request_size = config->server.max_request_size_bytes,
         event_batch_size = config->server.event_batch_size]() {
          pthread_setname_np(pthread_self(),
                             ("network-" + std::to_string(i)).c_str());
          while (!shutdown_requested.load(std::memory_order_relaxed)) {
            std::vector<struct epoll_event> events(event_batch_size);
            int eventCount;
            for (;;) {
              eventCount = epoll_wait(epollfd, events.data(), event_batch_size,
                                      1000 /* 1 second timeout */);
              if (eventCount == -1) {
                if (errno == EINTR) {
                  continue;
                }
                perror("epoll_wait");
                abort();
              }
              break;
            }

            if (eventCount == 0) {
              // Timeout occurred, check shutdown flag again
              continue;
            }

            for (int i = 0; i < eventCount; ++i) {
              // Take ownership from epoll: raw pointer -> unique_ptr
              std::unique_ptr<Connection> conn{
                  static_cast<Connection *>(events[i].data.ptr)};
              conn->tsan_acquire();
              events[i].data.ptr =
                  nullptr; // Clear epoll pointer (we own it now)
              const int fd = conn->fd;

              if (events[i].events & (EPOLLERR | EPOLLHUP | EPOLLRDHUP)) {
                // Connection closed or error occurred - unique_ptr destructor
                // cleans up
                continue;
              }

              if (events[i].events & EPOLLIN) {
                conn->readBytes(max_request_size);
              }

              if (events[i].events & EPOLLOUT) {
                bool done = conn->writeBytes();
                if (done) {
                  continue;
                }
              }

              if (conn->tasks.empty()) {
                // Transfer back to epoll instance. This thread or another
                // thread will wake when fd is ready
                events[i].events = EPOLLIN | EPOLLONESHOT | EPOLLRDHUP;
              } else {
                events[i].events = EPOLLOUT | EPOLLONESHOT | EPOLLRDHUP;
              }
              // Transfer ownership back to epoll: unique_ptr -> raw pointer
              conn->tsan_release();
              events[i].data.ptr =
                  conn.release(); // epoll now owns the connection
              int e = epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &events[i]);
              if (e == -1) {
                perror("epoll_ctl");
                abort(); // Process termination - OS cleans up leaked connection
              }
            }
          }
        });
  }

  std::atomic<int64_t> connectionId{0};

  // Accept threads from configuration
  int acceptThreads = config->server.accept_threads;
  for (int i = 0; i < acceptThreads; ++i) {
    threads.emplace_back([epollfd, i, sockfd, &connectionId]() {
      pthread_setname_np(pthread_self(),
                         ("accept-" + std::to_string(i)).c_str());
      // Call accept in a loop
      while (!shutdown_requested.load(std::memory_order_relaxed)) {
        struct sockaddr_storage addr;
        int fd = getAcceptFd(sockfd, &addr);
        if (fd == -1) {
          if (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK) {
            // TODO revisit
            std::this_thread::sleep_for(std::chrono::milliseconds(10));
            continue;
          }
          perror("accept4");
          continue;
        }
        auto conn = std::make_unique<Connection>(
            addr, fd, connectionId.fetch_add(1, std::memory_order_relaxed));
        // Transfer new connection to epoll ownership
        struct epoll_event event{};
        event.events = EPOLLIN | EPOLLONESHOT |
                       EPOLLRDHUP; // Listen for reads and disconnects
        conn->tsan_release();
        event.data.ptr = conn.release(); // epoll now owns the connection
        int e = epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event);
        if (e == -1) {
          perror("epoll_ctl");
          abort(); // Process termination - OS cleans up leaked connection
        }
      }
    });
  }

  for (auto &t : threads) {
    t.join();
  }

  return 0;
}